The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
As the area storage density in hard disk drives (HDDs) increases, the demand for a larger magnetoresistive effect has led to extensive research efforts worldwide. Particularly, a MgO barrier-based magnetic tunnel junction (MTJ) is currently being used in HDDs. In typical MgO-MTJs, band matching between a MgO barrier and adjacent magnetic layers is a requirement to obtain a high magnetoresistance (MR), which is closely related to the epitaxial relationship between the MgO barrier and adjacent layers. Generally, these adjacent layers are amorphous magnetic layers, such as CoFeB and the like. In order to obtain a high MR ratio in amorphous CoFeB/crystalline MgO/amorphous CoFeB MTJs, an annealing step is necessary in order to produce crystallized bcc CoFeB (100)/MgO(100)/crystallized bcc CoFeB (100). In a magnetic head, a free layer should produce a high MR and lower magnetostriction; especially in MgO-MTJ heads, the free layer includes the first magnetic layer with high spin polarization, which typically shows highly positive magnetostriction A common approach is to make a multilayer free layer with a thin, high-spin polarization layer next to the barrier layer and a relatively thick layer of NiFe alloy, which has negative magnetostriction. NiFe which has a Fe content of less than 10% is used as a negative magnetostriction free layer for some MgO-MTJ sensors. When the sputtered NiFe film is used as second free layer, it destroys the epitaxial relationship between the MgO barrier and the first free layer due to the highly textured fcc NiFe films which cause the crystallization to occur from the NiFe/first magnetic layer (generally a CoFeB layer) interface. This leads to a low MR. Currently, in order to solve this problem, pure Ta can be inserted between NiFe and the first magnetic layer to prevent the crystallization from occurring in the NiFe/first magnetic layer. However, a pure Ta layer reduces the magnetic coupling strength between NiFe and the first magnetic layer, and acts as an interface (impurity) which is believed to be a noise source.
Therefore, there is a need in the art for a MgO-MTJ that has sufficient band matching between the MgO barrier and adjacent magnetic layers, has a high MR, and does not succumb to the issues associated with conventional MgO-MTJ head designs.